Private messaging on backend only


I am wondering if it's possible to utlize the private messaging in wp-admin only -- with the inbox sitting in a page inside wp-admin, and nothing being added to the frontend?

Also, using the "capabilities" add-on, I tried to limit the users to only be able to send emails to the 'editor' role, but it does not seem to work.

I'd like to use this plugin as a way to allow authors to communicate with the editor(s) of the site via private messaging in the backend. Is this possible?

Thank you,